This present disclosure relates to thermal switches.
A thermal switch may be used for protection of an electrical installation connected to a power supply against an electrical fire caused by overheating of deficient electrical contacts such as switch contacts or wiring terminations. In particular, the thermal switch may be provided in proximity to an electrical plug, socket, switch or screw terminal etc. to detect an undue increase in temperature caused by a deficient contact. Upon detection of an undue increase in temperature the thermal switch causes an interruption of the power supply.
The thermal switch may be a device comprising first and second electrically conducting terminals configured such that the device is non-conducting in a first state, and conducting in a second state in response to a detection of a predetermined temperature. The predetermined temperature is, on the one hand, well above temperatures occurring during normal operation and, on the other hand, well below temperatures that may cause an electrical fire. The first and second terminals of the thermal switch may be connected to earth and neutral conductors or earth and live conductors to generate a fault, when the device is in the conducting state, that trips a residual current detector to interrupt the power supply.
WO 2006/125996 A1 discloses thermal switches capable of detecting when a build-up of heat occurs. In an embodiment, the terminals are separated by an electrically insulating spacer made of a material that melts at the predetermined temperature such that, when the spacer melts, the first and second terminals contact each other under a biasing force, thereby activating the thermal switch. Such a meltable material is—in principle—well suited for a thermal switch due to its precisely definable and known melting point. A thermal switch including such an electrically insulating spacer, however, requires a great biasing force for ensuring that the first and second terminals contact each other reliably when the spacer melts. Such great biasing force can alter the state of the insulating spacer prior to its melting temperature, therefore reducing the reliability of the insulating spacer over time.